Numerous biological substances are known in which the fractions or derivatives of these substances are strongly colored by compositions of tetrapyrrole structure such as, for example, heme or chlorophyls. These compounds are complex molecules formed of four pyrrole nuclei substitutes on the beta carbons and which are united between them, by alpha carbons, by the intermediary of the methanol radical-CH.dbd..
The substituents carried by the beta carbons of the pyrroles are, in particular, the groups of methyl, vinyl, propionyl (eventually estherified), or formal. In addition, in the chlorophyls, a methanyl group is connected to the beta carbon of a neighboring pyrrole to form a cyclopentanone cycle.
In addition, in hemoglobin and its derivatives, an atom of iron is bound to four pyrrole azotes. Similarly, the cholorphyls contain an atom of magnesium bound to four pyrrole azotes.
The presence in these compositions of strong colors is often undesirable in a number of products of animal or vegetable origin and satisfactory decoloring of these products is difficult.
The problems posed by decoloring of derivatives of blood are well known, and it is also known by specialists that analogous problems are present for decoloring substances containing other tetrapyrrole colorants, such as, for example, the chlorophyls or their derivatives.
One knows that the preparation and purification of the derivatives of blood presents problems of decoloring which are difficult to solve. In effect, the majority of blood derivatives are strongly colored by hemoglobin even if the hemoglobin is present in small quantities.
One knows that the red corpuscles of blood are capable of constituting a significant source of protein, only a small portion of which is recovered, principally for human or animal food, the rest being rejected as refuse.
This rejected large portion of blood products obtained from slaughtering, constitutes not only wasting of proteins of very high quality, but is also a significant source of pollution.
One knows that hemoglobin represents two tiers of proteins of blood and that its coloring is intense, which makes it very difficult to use the blood in food, with the exception of its traditional use in sausages.
The blood destined to be used in human food is usually centrifuged in a manner to separate the plasma (composed of colorless proteins) from cruor, which is the cellular solid residue constituted of about 95% hemoglobin. When the plasma is used in salted or frozen meat, all the cruor is rejected and wasted.
The problems of coloring of products of blood are due to the fact that the hemoglobin molecule comprises prosthetic groups called hemes which are the strongly colored complex molecules formed of four heterocyclic azote nuclei connected to an atom of iron. To obtain non-colored blood derivatives, the molecules of heme can be separated from the rest of the molecule (globin).
However, it is well known that the heme-globin bond is relatively strong. To rupture this bond acetone-containing hydrochloric acid has been used. The liberated heme dissolves in the acetone while the decolored protein precipitates; see, for example: LEWIS, U. J.; J. Biol. chem., 206 109 (1954).
However, the decoloring of hemoglobin by acetone is difficult to exploit industrially. In essence, the volumes of acetone necessary for complete decoloring are very high, on the order of 10 volumes of acetone for one volume of blood, and requires recycling of this organic solvent. In addition, the use of large volumes of acetone poses safety problems.
It has also been proposed to decolor hemoglobin by the use of diverse chemical transformations such as oxidation by oxygenated water. This method presents various disadvantages such as chemical modification of the proteins by the oxidation, and the formation of insoluble products.
Another method of decoloring consists of enzymatic hydrolysis of hemoglobin with production of two forms of peptides: the hemen peptides (colored); and the non-hemen peptides (colorless). The colorless peptides have been separated by ultrafiltration, gel-filtration or adsorption on active carbon; see, for example, French Patent Application No. 79 02940 (2,415,968) and the article by Jean REGNIER, R.T.V.A., November 1983, pages 29-35.
However, the techniques of decoloring based on hydrolysis of hemoglobin do not result in decoloring sufficient for certain applications, and involve a significant loss of peptides.